A campaign to use age-old powers to impeach Tony Blair for misleading the public over the Iraq war is being launched by a group of MPs on Thursday.

The power, last used in 1806, could in theory see Mr Blair charged with improper conduct in office but in practice has little chance of success.

US President Bill Clinton famously was impeached over the Monica Lewinsky scandal but was acquitted.

Plaid Cymru MP Adam Price is behind the Blair impeachment call.

Lords trial

Thursday's report has been produced by Dr Glen Rangwala, of Trinity College, Cambridge, and Dan Plesch, honorary fellow of Birkbeck College, University of London.

It has reportedly been backed by 11 MPs - nine of them Welsh and Scottish nationalists and two Conservatives, frontbencher Boris Johnson and ex-shadow minister Nigel Evans.

Price's idea has been branded a laughable stunt by MPs

The MPs are set to table a Commons motion calling for Mr Blair to go before Parliament to defend his record on Iraq.

The idea would be to get MPs to vote to set up a criminal trial of the prime minister, with the Lords acting as judges.

One of the last impeachment cases was of Warren Hastings, the final governor-general of India, who was acquitted by his trial.

The power can theoretically be used for "high crimes and misdemeanours beyond the reach of the law or which no other authority of the state will prosecute".

Mr Price is charging Mr Blair with:

Misleading Parliament and the country over Iraq

Negligence and incompetence over weapons of mass destruction

Undermining the constitution

Entering into a secret agreement with the US president.

'No joke'

Anti-war MP Mr Price told BBC 2's Newsnight his impeachment call was not just a stunt.

"It deserves to be taken seriously," he said. "What has happened over the last 18 months is there is strong, compelling evidence we were misled over the war."

On BBC Wales, he added: "If nothing else comes out of this, people will realise impeachment is still an active part of parliamentary law and a minister who misleads and refuses to resign, can be removed by Parliament through impeachment."

The prime minister has acknowledged there were intelligence errors in the run-up to the Iraq war but denies misleading people.

He stresses the Butler and Hutton inquiries cleared him of deception or improper dealings.

'Silly'

Labour MP and former minister Keith Vaz told Newsnight: "This is a silly story for the end of the silly season."

Mr Vaz said the evidence in the academics report was thin and questions over the Iraq war had been raised numerous times in Parliament, as well as in a string of inquiries.

"This matter has been put before the nation day after day over the last few years," said Mr Vaz. "All these reports have exonerated the government and it's time to move on."

Donald Anderson, chairman of the Commons foreign affairs committee, called the impeachment call a "political stunt" and a "no-hoper in legal terms".

"Any judge would smell the politics of this and throw it out at the first opportunity," he told BBC Wales."

Obsolete?

Impeachment has mostly been used in Britain during the 1640s Civil War.

A special parliamentary committee in 1999 said "the circumstances in which impeachment has taken place are now so remote from the present that the procedure may be considered obsolete".

Lord Norton of Louth, professor of government at Hull University, told BBC News Online: "It is still on the books so it's open technically for the Commons to vote for impeachment."

But in reality, it was more a way of raising an issue, with MPs unlikely to vote for the measure, he said.